Although the chemical transformation of CO₂ has been achieved in industry, the reaction requires high pressure and elevated temperature because of the chemical inertness of CO₂. Up to now, the investigation of the active phase of non-noble catalysts in CO₂ hydrogenation is still at the rudimentary stage.Jie Zeng's group from USTC incorporated N atoms into Co catalysts to synthesize Co₄N catalysts. In CO₂ hydrogenation, Co₄N catalysts exhibited a turnover frequency (TOF) of 25.6 h^-1 under 32 bar at 150 ^oC, which was 64 times as high as that of Co catalysts. The activation energy for Co₄N catalysts was 43.3 kJ mol^-1, less than half of that (91.4 kJ mol^-1) for Co catalysts. Further mechanistic studies collaborated with the photoemission end-station at beamline BL10B in the NSRL revealed that Co₄NH_x was formed by adsorbing H atoms on N atoms in Co₄N nanosheets in the presence of H₂. The amido-hydrogen atoms in Co₄NH_x directly added to CO₂ to form HCOO* as the intermediates. In addition, the adsorbed H₂O* was found to activate the amido-hydrogen atoms via the interaction of hydrogen bonds, which facilitated the hydrogenation process. This work not only provides a way to engineer efficient, low-cost catalysts for CO₂ hydrogenation via the incorporation of N atoms, but also advances our understanding of active phase of Co-based catalysts.This work has been published on Nature Energy (Nature Energy 2017, 2, 869-876.).

Illustration of CO₂ hydrogenation over Co₄N catalysts